Copper base alloys have been extensively utilized in tubing for heat exchanger applications. These alloys, in particular the copper-nickel alloys, have found wide acceptance due to their good balance of corrosion resistance and mechanical properties. In particular, such alloys as Alloy 706 and 715 (containing, respectively, 10% and 30% nickel in a copper base) are used in tubular form in surface condenser heat exchangers in power generating plants, particularly those using polluted waters containing sulfides. In such environments, Alloy 706 has been shown to have the best overall performance of any commercially available copper alloy tubing material. These alloys, although widely used, do present difficulties of their own. In particular, at least 10% nickel is usually necessary in the alloys to achieve good corrosion resistance. This tends to make the alloys quite expensive and therefore uncompetitive with other non-copper alloy systems.
Various alloy systems have been developed to overcome the high cost of the copper-nickel alloy systems. These alloy systems have generally not been able to provide the high corrosion resistance properties of the copper-nickel alloys in heat exchanger applications. Alloy systems have been developed for their corrosion resistance properties which utilize varied alloy additions for such properties. For example, U.S. Pat. Nos. 3,627,593, 3,703,367 and 3,713,814 all utilize various additions of nickel to copper-zinc alloy bases to provide increased corrosion resistance along with increased strength properties. U.S. Pat. No. 3,627,593 utilizes a basic copper-nickel-zinc alloy to provide these properties while U.S. Pat. No. 3,703,367 utilizes titanium additions together with aluminum or nickel additions or both to copper-zinc alloy bases to provide these increases in properties to the alloy systems. This particular patent specifically utilizes these materials in water tubing. U.S. Pat. No. 3,713,814 utilizes a copper-zinc base to which are added various alloying elements such as lead, nickel, manganese and aluminum, among others, to provide an alloy system which exhibits good resistance against corrosion.
Various Japanese scientists have studied the effect of additives to particular copper alloy systems to determine the effect of these additives upon corrosion properties of the systems. In particular, Nagasaki et al. have indicated in their report "Effect of Additives on Dezincification Rate of Alpha-Brass at High Temperature in Vacuum" in the Journal of the Japan Institute of Metals, Volume 34, No. 3 on Pages 343 to 347 that various elements including iron, cobalt and nickel may be added in ranges up to 1 or 2% to prevent the dezincification of copper base alloys. In each of the examples within this particular reference, the zinc content of each specimen is 30% by weight. Otsu et al. have discovered in their "Study of Corrosion of Copper Alloys in High Temperature Water and Steam" in the Sumitomo Light Metal Technical Reports issued in January, 1960, January, April, July and October, 1964 and in July, 1965 that the addition of small amounts of such elements as iron, nickel, arsenic, antimony or phosphorus to a copper alloy containing 30% by weight zinc has some beneficial effects upon the corrosion resistance of the alloy. None of these references, either the U.S. patents or the Japanese articles, disclose the particular alloy system which will be disclosed in the present specification.
Therefore, it is a principal object of the present invention to provide an alloy system which is highly resistant to corrosion without being high in cost.
It is a further object of the present invention to provide an alloy system as aforesaid which demonstrates increased resistance to corrosion in waters known to attack commercially available corrosion resistant alloys and particularly in sulfide containing waters.
It is yet a further object of the present invention to provide an alloy system as aforesaid which retains single phase properties within the alloy structure after processing to increase corrosion resistance properties.
Further objects and advantages of the present invention will become apparent from a consideration of the following specification.